Compact in-line reflective optical beam expander or reducer with adjustable focus

A system comprising:

• a laser configured to generate an input optical beam;
• and
• an in-line reflective optical system configured to receive the input optical beam and provide an output optical beam, the in-line reflective optical system comprising:
• first and second powered mirrors aligned back-to-back, the first powered mirror configured to reflect the input optical beam as a first intermediate beam;
• and
• first and second reflective surfaces respectively configured to reflect the first intermediate beam as a second intermediate beam and to reflect the second intermediate beam as a third intermediate beam, the second powered mirror configured to reflect the third intermediate beam as the output optical beam;
• wherein a spacing between the first and second reflective surfaces and the first and second powered mirrors is adjustable to control a focus of the output optical beam without introducing boresight error in the output optical beam.

A method comprising:

• reflecting an input optical beam as a first intermediate beam using a first powered mirror;
• reflecting the first intermediate beam as a second intermediate beam using a first reflective surface;
• reflecting the second intermediate beam as a third intermediate beam using a second reflective surface;
• and
• reflecting the third intermediate beam as an output optical beam using a second powered mirror;
• wherein the first and second powered mirrors are aligned back-to-back;
• and
• wherein a spacing between the first and second reflective surfaces and the first and second powered mirrors is adjustable to control a focus of the output optical beam without introducing boresight error in the output optical beam.